Photodetectors are a fundamental component of optoelectronic systems, converting an intensity modulated mode of optical radiation into a voltage signal. A characteristic of many current high-speed photodetectors is that they have a relatively low saturation power, often on the order of 5 mW or less. This is a significant limitation, not only because optical powers higher than this can't be used, but also because at even lower optical powers the response becomes nonlinear. This interferes in many important aspects of RF system performance, such as the spur-free dynamic range and the output OIP2 and OIP3 intercept points.
A natural way to increase the saturation power of a photodetector would be to make the active area larger. Indeed, this is the mechanism by which high power photodetectors are usually built. However, this creates significant limitations on device response time, due to larger areas that carriers must traverse to reach the output electrodes.
Waveguide integrated photodetectors for near-infrared radiation (near 1550 nm) typically use an evanescently coupled semiconductor material that has a bandgap past 1550 um, such as Germanium or a III-V semiconductor, often with lengths on the order of 20-30 um. However, the limited area of these photodetectors suggests that saturation is likely no better than what is found in conventional photodetectors.